Process and apparatus for removing H2 S from gas streams

ABSTRACT

A gas stream containing CO 2  and H 2  S is contacted with an alkanolamine in a contacting zone. The rich solution is then selectively stripped in a stripping zone to produce a gas stream containing a higher CO 2  :H 2  S mole ratio than the initial stream. This stream can be recycled to the alkanolamine contacting zone. The partially stripped solution can be introduced into another stripping zone to provide a third gas stream which is rich in H 2  S and lean in CO 2  suitable as feed for a Claus Unit and a lean alkanolamine solution which can be recycled to the contacting zone.

BACKGROUND OF THE INVENTION

The invention relates to the treatment of gas streams. In another aspectthe invention relates to treating an acid gas stream with analkanolamine solution. In yet another aspect, the invention relates toselectively regenerating alkanolamine solution which has been contactedwith acid gases.

The use of amines for the removal of hydrogen sulfide and carbon dioxidefrom gas streams is well known. Triethanol amine (TEA) was the first ofthe ethanol amines to become commercially available. It was used in theearly gas treating plants. This amine has generally been displaced ingas treating plants by diethanol amine (DEA) and monoethanol amine(MEA). The advantage to the use of DEA and MEA lies in their lowermolecular weights and their ability to more completely absorb hydrogensulfide from the gas. Of these three amines, monoethanol amine isgenerally preferred because of its ability to produce sweet gas streamswith extremely low hydrogen sulfide levels under the same operatingconditions.

Frequently, large quantities of carbon dioxide occur in gas streamscontaining hydrogen sulfide. When complete hydrogen sulfide removal isattained, processes utilizing MEA and DEA also absorb essentially all ofthe carbon dioxide. There are frequent occasions when it would bedesirable to send a major portion of the carbon dioxide with the treatedgas stream while removing essentially all of the hydrogen sulfide. Thecurrent need for processes to selectively remove hydrogen sulfide fromgas streams can be summarized as follows:

(1) The high cost of energy required to regenerate the amine solutioncan be reduced if less carbon dioxide is absorbed.

(2) The Claus process requires a high ratio of hydrogen sulfide tocarbon dioxide for most economic operation, otherwise capital andoperating costs for a Claus plant could soar.

(3) As environmental restrictions become more stringent, many of the lowhydrogen sulfide to carbon dioxide streams now being flared will have tobe treated before flaring.

(4) Synthetic natural gas streams are very high in carbon dioxide andmust be de-sulfurized before feeding to any known catalytic conversionprocess to produce high BTU fuel.

OBJECTS OF THE INVENTION

It is an object of this invention to selectively remove H₂ S from gasstreams also containing CO₂.

It is another object of this invention to provide a process which can beutilized to prepare feed for a Claus plant so that H₂ S can be convertedto sulfur.

It is another object of the invention to provide a process for treatinggas streams containing a low H₂ S:CO₂ mole ratio.

It is yet another object of this invention to provide a low-pressureprocess for the production of high purity H₂ S.

It is yet another object of the invention to provide a process which canbe employed to de-sulfurize synthetic natural gas streams rich in carbondioxide.

SUMMARY OF THE INVENTION

According to one embodiment of the present invention, an apparatuscomprises a first column having an upper end and a lower end with aliquid inlet and vapor outlet adjacent its upper end and a vapor inletand liquid outlet adjacent its lower end; a second column having anupper end and a lower end with a vapor outlet adjacent its upper end, aliquid outlet adjacent its lower end, and a liquid inlet between itsupper end and its lower end; a first conduit means connecting the liquidoutlet adjacent the lower end of the first column with a liquid inletbetween the upper end and the lower end of the second columns; a thirdcolumn having an upper end and a lower end with a vapor outlet adjacentits upper end, a liquid outlet adjacent its lower end, and a liquidinlet between its upper end and its lower end; a second conduit meansconnecting the liquid outlet adjacent the lower end of the second columnwith the liquid inlet between the upper end and the lower end of thethird column; and a third conduit means connecting the liquid outletadjacent the lower end of the third column with the liquid inletadjacent the upper end of the first column. Desirably, the first columnserves as an alkanolamine contacting zone, the second column serves as aselective stripping zone for producing an overhead stream relativelyrich in CO₂ which can be recycled to the contacting zone and a bottomsstream which is relatively rich in H₂ S and can be conveyed to the thirdcolumn. The third column can serve to substantially regenerate thealkanolamine solution, producing an overhead stream rich in H₂ S andlean in CO₂ suitable for feed to a Claus unit, or to another unit forthe production of high-purity, e.g. greater than 99 mole %, H₂ S, and abottoms stream comprising lean alkanolamine solution which can berecycled to the contacting zone.

According to another aspect of the present invention, a processcomprises contacting a first gas stream containing CO₂, H₂ S and atleast one hydrocarbon with a solution of at least one alkanolamine in acontacting zone; withdrawing a rich solution of at least onealkanolamine from the contacting zone which is rich in H₂ S and CO₂ fromthe first gas stream; introducing the rich solution into a separationzone; selectively stripping the rich solution in the separation zone toproduce a second gas stream issuing from the separation zone whichcontains a higher CO₂ :H₂ S mole ratio than the first stream; andconveying the second gas stream into an alkanolamine contacting zonewhich can be the same as or different from the first zone. By conveyingthe second gas stream to the alkanolamine contacting zone, a greaterportion of the CO₂ contained in the first gas stream can be slipped andstill meet H₂ S removal requirements for the treated stream. Byselectively stripping the rich solution in the separation zone, apartially stripped solution can be obtained with contains a higher H₂S:CO.sub. 2 mole ratio than the rich solution from the contacting zone.

In accordance with yet another aspect of the present invention, aprocess comprises contacting a first gas stream containing H₂ S, CO₂ andat least one hydrocarbon with a lean alkanolamine solution in acontacting zone; withdrawing a rich alkanolamine solution from thecontacting zone which contains at least a portion of the H₂ S and CO₂from the first gas stream; introducing the rich alkanolamine solutioninto a first stripping zone; selectively stripping the rich alkanolsolution in the first stripping zone to produce a second gas streamissuing from the stripping zone which contains a higher CO₂ :H₂ S moleratio than the first gas stream; withdrawing a selectively strippedalkanolamine solution from the first stripping zone; said selectivelystripped alkanolamine solution containing a higher H₂ S:CO₂ mole ratiothan the rich alkanolamine solution from the contacting zone;introducing the selectively stripped solution into a second strippingzone; and stripping the selectively stripped solution to produce a thirdgas stream which is rich in H₂ S and lean in CO₂. By utilizing twostripping zones, a third gas stream can be obtained which can bedesirably processed in a Claus unit, due to its high H₂ S:CO₂ moleratio. If desired, the second gas stream can be recycled to thecontacting zone for removal of residual H₂ S and additional slippage ofCO₂.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE illustrates schematically certain features of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

According to the invention, a treating vessel such as a column 2 has anupper end 4 and lower end 6. A liquid inlet 8 and a vapor outlet 10 openinto the column 2 adjacent its upper end 4 and a vapor inlet 12 and aliquid outlet 14 open into the column 2 adjacent its lower end 6. Asecond column 16 having an upper end 18 and lower end 20 is providedwith a liquid outlet 21 adjacent its lower end, a vapor outlet 22adjacent its upper end and a liquid inlet 24 between its upper end 18and its lower end 20. A first conduit means 26 connects the liquidoutlet 14 adjacent the lower end 6 of the first column 2 with the liquidinlet 24 between the upper end 18 and the lower end 20 of the secondcolumn 16. A third column 28 having an upper end 30 and a lower end 32is provided with a vapor outlet 34 adjacent its upper end 30, a liquidoutlet 36 adjacent its lower end 32 and a liquid inlet 38 between itsupper end 30 and its lower end 32. A second conduit means 40 connectsthe liquid outlet 21 adjacent the lower end 20 of the second column 16with the liquid inlet 38 between the upper end 30 and the lower end 32of the third column 28. A third conduit means 42 connects the liquidoutlet 36 adjacent the lower end 32 of the third column 28 with theliquid inlet 8 adjacent the upper end 4 of the first column 2.

Preferably, the first column 2 is further provided with a second vaporinlet 44 between its upper end 4 and its lower end 6. A fourth conduitmeans 46 connects the vapor outlet 22 adjacent the upper end 18 of thesecond column 16 with the second vapor inlet 44 opening into the firstcolumn 2 between its upper end 4 and its lower end 6.

A reboiler means 52 is operably connected to the lower end 20 of thesecond column 16, while a reboiler means 54 is operably connected to thelower end 32 of the third column 28. Preferably, the reboilers 52 and 54are of the thermosiphon type. Preferably, the second column 16 and thethird column 28 are provided with a means 56 and 58 respectively forreturning reflux to the upper portions of the columns. From the vaporoutlet 22 in the upper portion 18 of the column 16, there extends aconduit 60 which, after passing into operable association with acondensor 48, empties into a reflux accumulator 62. A conduit means 64establishes a flow path from a lower portion of the accumulator 62 tothe upper portion 18 of the column 16. A pump 66 is associated with theconduit 64 for causing liquid flow from the accumulator 62 to the upperportion of the column 18. A conduit means 61 establishes a flow pathfrom an upper portion of the accumulator 62 to the inlet 44 of thecolumn 2. A compressor 50 is associated with the conduit 61 for causingvapor flow from the upper portion of the accumulator to the inlet 44 ofthe column 2. The means 46 preferably comprises the conduit 60,condensor 48, accumulator 62, conduit 61, and compressor 50. A conduit68 extends from the vapor outlet 34 in the upper portion 30 of the thirdcolumn 28 and, after passage through a condensor 70 empties into anaccumulator 72. A conduit 74 establishes a flow path between a lowerportion of the accumulator 72 and the upper portion 30 of the thirdcolumn 28. A pump 76 is operably connected to the conduit 74 for causingliquid flow from the accumulator 72 to the upper portion 30 of thecolumn 28.

It is preferred that at least one heat exchange means be associated withthe conduit means 42 for cooling fluid flow therethrough. In theillustrated embodiment, a portion of the conduit means 26 passes in heatexchange relationship with the conduit means 42 at heat exchanger 78. Acooler 80 is further disposed in the conduit 42 between the heatexchanger 78 and the liquid inlet 8 in the upper portion 4 of the column2 for cooling liquid flow through the conduit means 42 to a desiredtemperature.

A conduit 90 connected to a vapor outlet 92 in an upper portion of theaccumulator 72 can be connected to a Claus unit, not shown, if desired.A conduit 94 is connected to the vapor inlet in the lower portion 6 ofthe column 2, and will usually be connected to a pipeline system or acracking zone not shown. Treated desulfurized gas is withdrawn from thezone 2 via 96 and is utilized as desired.

To help eliminate corrosion problems, the unit can be constructed of asuitable corrosion-resistant material, such as 304 stainless steel. Thecolumn 2 can be an absorber fitted with sieve trays, liquid downcomersand overflow weirs. The columns 16 and 28 can be packed with a suitablematerial to increase available surface area, such as 5/8" stainlesssteel Pall rings.

In operation, a gas stream 94 containing CO₂, H₂ S, and at least onehydrocarbon is contacted with a solution of at least one alkanolamine ina contacting zone 2, usually an absorber. The first gas stream couldhave its origin, for example, in a sour natural gas field, in which caseit would probably contain both H₂ S and CO₂ at moderate concentrationsin a range of 0.05 mole % to 8 mole %, for example; or from a thermalcracking unit producing unrefined synthetic natural gas, in which eventstream 94 would likely contain a greater concentration of CO₂ than H₂ Swhich can range up to 30-35 molar percent CO₂ plus H₂ S (acid gases). Itis anticipated that the present invention will have its greatest utilityin treating gas streams containing a relatively high ratio of CO₂ to H₂S, for example, a CO₂ :H₂ S mole ratio of greater than about 1:1,although where very high purity H₂ S is desired, the feed stream willusually contain a CO₂ :H₂ S mole ratio of about 1:2 or less. Forexample, a synthetic gas blend containing hydrogen, ethylene, carbondioxide, and hydrogen sulfide might exhibit a mole ratio of CO₂ :H₂ S ofabout 8.8:1, while a natural gas blend might exhibit a CO₂ :H₂ S moleratio of 0.3:1 up to 4:1.

The alkanolamine employed in the process of the present inventionpreferably is selected from the group consisting methyldiethanolamine(MDEA) and n-propyldiethanolamine (PDEA). N-propyldiethanolamine is lessexpensive than methyldiethanolamine, but regeneration of PDEA solutionsrequires more energy.

Conditions in the absorber can vary widely. Preferably, contact betweenthe first gas stream and the solution of alkanolamine is incountercurrent fashion, the solution of alkanolamine flowing in vigorousvapor contact in the absorber. The gas stream 94 is generally contactedin the contacting zone with between about 10 and about 1,000 moles ofalkanolamine for each mole of H₂ S which it contains for good results.The alkanolamine solution employed will normally contain between about 5and about 50 weight percent of the alkanolamine although higher or lowerconcentrations can be utilized if desired. Conditions in the absorber 2will generally include a temperature within the range of from about 0°to about 100° C. and a pressure within the range of from about 0° toabout 100 psig (pounds per square inch, gauge) (100-800kilopascals,kPa).

From the absorber 2, there is withdrawn a rich solution by the conduitmeans 26 of the at least one alkanolamine solution which is rich in H₂ Sand CO₂ from the first gas stream. This rich solution is introduced intoa separation zone 16 and selectively stripped therein to produce asecond gas stream 60 issuing from the separation zone 16 which containsa higher CO₂ :H₂ S mole ratio than the first stream 94. The second gasstream 60 can be conveyed into an alkanolamine contacting zone which isthe same as or different from the first zone 2. In the embodimentillustrated, after being partially condensed for reflux, a portion ofthe second gas stream passes through compressor 50 and is reintroducedinto the zone 2, preferably at a position in the absorber at which thegas phase contains the same CO₂ :H₂ S mole ratio as the second gasstream.

It is desirable that the second gas stream be introduced into thealkanolamine contacting zones at a point above that at which the firstgas stream is introduced because CO₂ slippage is primarily a function ofthe number of absorber trays and the absorber pressure. Since pressurein the unit is constant, reducing the number of trays between the pointinlet 44 at which the second stream is introduced and the purified gasstream 96 is withdrawn increases CO₂ slippage, where slippage is definedas the passage of CO₂ from the unit with the treated gas stream aspercent of total CO₂ in feed. Another reason for introducing the secondstream into an intermediate or upper section of the absorber is thathigh concentrations of carbon dioxide flowing upwards through theabsorber tends to displace residual hydrogen sulfide from the leansolvent at the top of the absorber which can result in higherconcentrations of hydrogen sulfide in the treated gas than would beexpected. The efficiency of the individual trays is at least a functionof the CO₂ :H₂ S mole ratio and tray efficiency decreases as the ratioincreases. This is attributed to the displacement action of carbondioxide on the residual hydrogen sulfide in the lean solvent. The secondgas stream with a high CO₂ :H₂ S mole ratio should thus be introduced inthe upper section of the absorber. This will minimize the detrimentaleffect of H₂ S displacement by CO₂. The result is a lessening of thedetrimental effect of a high CO₂ :H₂ S mole ratio on overall absorber H₂S removal efficiency.

Generally speaking, the gas stream 94 to be treated will contain somehydrocarbon. Hydrocarbons containing greater than about 3 to 4 carbonatoms have a tendency to become dissolved in the alkanolamine solvent,and become stripped from the solvent during regeneration. This can causeoperating problems, such as foaming. It is thus preferable, whenhydrocarbon is present, that the gas stream to be treated contain ahydrocarbon which has from about 1 to about 3 carbon atoms. However,when the stream 44 contains heavier hydrocarbons, they may be recoveredin the treated gas to increase its BTU value, rather than the acid gas,due to recycle via line 61.

Because one of the purposes of selectively stripping the alkanolaminesolution is to produce a selectively stripped aqueous phase whichcontains a higher H₂ S:CO₂ mole ratio than the rich solution issuingfrom the absorber, the selective stripping should be conducted underconditions less severe than those required to remove a major portion ofthe H₂ S from the rich alkanolamine solution. Typically, it isanticipated that the selective stripper will be operated at a pressureof between about 0 and about 40 psig, (100-450 kPa) and a temperature offrom about 220° and about 260° F. (104°-127° C.).

According to another aspect of the present invention, a processcomprises contacting a first gas stream containing H₂ S, CO₂ and atleast one hydrocarbon with a lean alkanolamine solution in a contactingzone. For example, a gas stream carried by the conduit 94 can beintroduced into the absorber 2 at inlet 12 and contacted therein withlean alkanolamine solution flowing downward through the absorber fromliquid inlet 8 to liquid outlet 14. The rich alkanolamine solution,which contains at least a portion of the H₂ S and CO₂ from the first gasstream is withdrawn from the contacting zone, for example, throughoutlet 14, and conveyed via conduit means 26 to a first stripping zone,such as the selective stripper 16 and introduced thereinto. In theselective stripping zone 16, the rich alkanolamine solution isselectively stripped to produce a second gas stream for example, 60,which issues from the stripping zone and contains a higher CO₂ :H₂ Smole ratio than the first gas stream 94. The selectively stripped,partially regenerated, alkanolamine solution is withdrawn from the firststripping zone, for example, through outlet 21 and introduced into asecond stripping zone, for example, the column 28, via conduit means 40.The selectively stripped alkanolamine solution will exhibit a higher H₂S:CO₂ mole ratio than the rich alkanolamine solution 26 from thecontacting zone 2. In the second stripping zone, the selectivelystripped solution is further stripped to produce a third gas stream,such as 90 which is rich in H₂ S and lean in CO₂. This gas stream 90 canbe suitably conveyed to a Claus unit. If desired, at least a portion ofthe stream 90 can be fed to a second unit as shown in the drawing, i.e.be utilized as the feed stream 94 for a second unit in series with thefirst, to result in the production of high purity H₂ S.

Where the feedstream 94 contains a significant concentration ofhydrocarbons having greater than about 3 carbon atoms, the presentprocess provides a recycle mechanism whereby the heavy hydrocarbons canbe withdrawn from the unit via conduit 96, rather than along with theacid gases from conduit 90. The heavy hydrocarbon components can thusincrease the BTU value of the treated gas, rather than possiblycontaminating valuable catalyst in a Claus unit. Thus, it is desirablewhen practicing this embodiment of the invention that the second gasstream 61 be conveyed to the absorber 2 such as at vapor inlet 44. Inany event, recycling of the stream 60 to the absorber can result in theproduction of increased purity H₂ S and is desirable for that reason.

Alkanolamine solution can be withdrawn from the second stripping zone 28which is lean in H₂ S and CO₂ and be introduced into the absorber 2 asat inlet 8 for contacting the first gas stream 94, and conservingmaterials. Where these steps are taken, a treated gas stream can bewithdrawn from the absorber 2, such as at conduit 96 which contains CO₂,at least one hydrocarbon, a minor amount of H₂ S, and a much higher CO₂:H₂ S mole ratio than the first gas stream. Preferably, the gas stream96 will exhibit a CO₂ :H₂ S mole ratio of about 100:1 or greater.Environmental considerations arising from the combustion of such a gasstream can thus be marketedly decreased.

The invention is illustrated by the following examples.

EXAMPLE 1

During operation of a pilot plant unit, it was observed duringregeneration of the MDEA solvent that the CO₂ and H₂ S were stripped todifferent degrees at various stripping conditions. For example,regenerating rich MDEA solution at different conditions in a stripperhaving a four inch diameter, a 20 foot length, filled with 5/8"stainless steel Pall rings and fitted with a steam reboiler produced thefollowing results:

                  TABLE I                                                         ______________________________________                                        Strip-                                                                        per                                                                           Kettle                                                                              Stripper Rich Solvent                                                                              Lean Solvent                                                                            Percent                                  Temp. Pressure Wt. %   Wt. % Wt. % Wt. % Removed                              F.°                                                                          PSIG     H.sub.2 S                                                                             CO.sub.2                                                                            H.sub.2 S                                                                           CO.sub.2                                                                            H.sub.2 S                                                                          CO.sub.2                        ______________________________________                                        231   9.7      0.95    2.4   0.85  0.98  10.5 59.2                            234   10       1.06    2.8   0.73  0.76  31.1 72.9                            241   10       0.76    1.4   0.38  0.19  50.0 86.4                            ______________________________________                                    

The runs show that the degrees to which H₂ S and CO₂ are stripped fromrich MDEA solution are dependent on stripper temperature.

EXAMPLE II (Calculated)

Runs 1-8 are conducted under the conditions and with the ultimateresults shown in Table II. Calculated material balances are shown byTable III. In this example, both strippers are hypothetically operatingat 10 psig and the absorber is operating at 40 psig. The leanalkanolamine solution is to comprise 30 wt. % MDEA. The hypotheticalfeed stream contains a higher than normal (for natural gas) CO₂ :H₂ Smole ratio, such as might be recovered in the effluent from a pyrolysisreaction.

EXAMPLE III (Calculated)

Runs 9-13 are conducted under the conditions and with the ultimateresults shown in Table IV. Calculated material balances are shown byTable V. This example shows the processing of a gas stream containingabout 6.5 mole % acid gases and a CO₂ :H₂ S mole ratio of about 4:1, andis thus representative of the processing of many sour natural gasstreams. The strippers are hypothecated to be operating at 10 psig andthe absorber at 40 psig with 30 wt % MDEA in the lean solvent.

EXAMPLE IV (Calculated)

This example is to demonstrate the utility of the invention for theproduction of high purity H₂ S suitable for chemical use without goingthrough high pressure distillation. The entire operation is conducted atlow pressure. In this example, both strippers and the absorber areoperating at 10 psig. The lean solvent comprises about 30 wt% MDEA. Thefeed to the absorber comprises 100% acid gas, 30 mole % CO₂ and 70 mole% H₂ S, such as might be present in a slip stream from the feed streamto a Claus Unit. A suitable feed stream could be all or a portion of theproduct from run 4 of Example II, for example.

Runs 14-19 are conducted under the conditions and with the ultimateresults shown in Table VI. Calculated material balances are shown byTable VII. In runs 14-16, the overhead from the first stripper 61 isrecycled to the absorber. In runs 17-19 the overhead is not so recycled.Under the hypothetical conditions, recycle of the stream 60 wasnecessary to achieve a product purity of greater than 99%.

                                      TABLE II                                    __________________________________________________________________________    CONDITIONS                                                                        First Kettle                                                                        Second Kettle                                                                         Solvent:Acid Gas                                                                       Solvent Circulation                                                                      H.sub.2 S Product                                                                       CO.sub.2 Passed               Run #                                                                             (52) (°F.)                                                                   (54) (°F.)                                                                     (GAL/SCF)                                                                              (GAL/100 moles feed)                                                                     (mole %)  (mole %)                      __________________________________________________________________________    1   230   245     1.3843   12437      60.9      96.0                          2   232   245     1.3845   12603      63.7      96.5                          3   234   245     1.3846   12804      66.9      96.9                          4   236   245     1.3847   13063      70.4      97.4                          5   238   245     1.3849   13426      74.3      97.9                          6   240   245     1.3850   13992      78.7      98.3                          7   242   245     1.3851   15062      83.6      98.9                          8   244   245     1.3853   17905      88.6      99.3                          __________________________________________________________________________

                                      TABLE III                                   __________________________________________________________________________    MATERIAL BALANCES (moles)                                                              Stream No.                                                           Run      94   61        42     96      26     40      90                      No.      Feed Gas                                                                           First Stripper OHP                                                                      Lean Solvent                                                                         Absorber OHP                                                                          Rich Solvent                                                                         1st Stripper                                                                          2nd Stripper            __________________________________________________________________________                                                          OHP                         CO.sub.2                                                                           21.0 1.318     0.044  20.165  2.197  0.879   0.835                       CH.sub.4+                                                                          77.7 3.625     0      77.7    3.625  0       0                           H.sub.2 S                                                                          1.3  0.052     0.078  0.0004  1.430  1.378   1.300                       TOTAL                                                                              100.0                                                                              4.995     0.122  97.865  7.252  2.257   2.135                   2                                                                                 CO.sub.2                                                                           21.0 1.424     0.039  20.26   2.203  0.778   0.740                       CH.sub.4+                                                                          77.7 3.634     0      77.7    3.634  0       0                           H.sub.2 S                                                                          1.3  0.258     0.078  0.0004  1.635  1.378   1.300                       TOTAL                                                                              100.0                                                                              5.316     0.117  97.960  7.472  2.156   2.040                   3                                                                                 CO.sub.2                                                                           21.0 1.531     0.034  20.356  2.208  0.677   0.644                       CH.sub.4+                                                                          77.7 3.644     0      77.7    3.644  0       0                           H.sub.2 S                                                                          1.3  0.532     0.078  0.0004  1.909  1.378   1.300                       TOTAL                                                                              100.0                                                                              5.707     0.112  98.056  7.761  2.055   1.944                   4                                                                                 CO.sub.2                                                                           21.0 1.639     0.029  20.453  2.214  0.575   0.547                       CH.sub.4+                                                                          77.7 3.654     0      77.7    3.654  0       0                           H.sub.2 S                                                                          1.3  0.916     0.078  0.0004  2.293  1.378   1.300                       TOTAL                                                                              100.0                                                                              6.209     0.107  98.153  8.161  1.953   1.847                   5                                                                                 CO.sub.2                                                                           21.0 1.747     0.023  20.550  2.220  0.473   0.450                       CH.sub.4+                                                                          77.7 3.663     0      77.7    3.663  0       0                           H.sub.2 S                                                                          1.3  1.494     0.078  0.0004  2.871  1.378   1.300                       TOTAL                                                                              100.0                                                                              6.904     0.101  98.250  8.754  1.851   1.750                   6                                                                                 CO.sub.2                                                                           21.0 1.856     0.018  20.648  2.226  0.370   0.352                       CH.sub.4+                                                                          77.7 3.673     0      77.7    3.673  0       0                           H.sub.2 S                                                                          1.3  2.460     0.078  0.0004  3.837  1.377   1.300                       TOTAL                                                                              100.0                                                                              7.989     0.096  93.348  9.736  1.747   1.652                   7                                                                                 CO.sub.2                                                                           21.0 1.965     0.013  20.746  2.232  0.267   0.254                       CH.sub.4+                                                                          77.7 3.683     0      77.7    3.683  0       0                           H.sub.2 S                                                                          1.3  4.385     0.078  0.0004  5.755  1.370   1.292                       TOTAL                                                                              100.0                                                                              10.033    0.091  98.446  11.670 1.637   1.546                   8                                                                                 CO.sub.2                                                                           21.0 2.075     0.008  20.845  2.238  0.163   0.155                       CH.sub.4+                                                                          77.7 3.693     0      77.7    3.693  0       0                           H.sub.2 S                                                                          1.3  9.678     0.073  0.0004  10.961 1.284   1.211                       TOTAL                                                                              100.0                                                                              15.446    0.081  98.545  16.892 1.447   1.366                   __________________________________________________________________________

                                      TABLE IV                                    __________________________________________________________________________    CONDITIONS                                                                        First Kettle                                                                        Second Kettle                                                                         Solvent:Acid Gas                                                                       Solvent Circulation                                                                      H.sub.2 S Product                                                                       CO.sub.2 Passed               Run #                                                                             (52) (°F.)                                                                   (54) (°F.)                                                                     (GAL/SCF)                                                                              (GAL/100 moles feed)                                                                     (mole %)  (mole %)                      __________________________________________________________________________     9  230   245     1.3845   3737       87.6      96.5                          10  230   245     1.3846   3895       89.1      96.9                          11  230   245     1.3847   4111       90.6      97.4                          12  230   245     1.3849   4430       92.1      97.9                          13  230   245     1.3850   4951       93.7      98.3                          __________________________________________________________________________

                                      TABLE V                                     __________________________________________________________________________    MATERIAL BALANCES (moles)                                                              Stream No.                                                           Run      94   61        42     96      26     40      90                      No.      Feed Gas                                                                           First Stripper OHP                                                                      Lean Solvent                                                                         Absorber OHP                                                                          Rich Solvent                                                                         1st Stripper                                                                          2nd Stripper            __________________________________________________________________________                                                          OHP                      9                                                                                CO.sub.2                                                                           5.2  0.353     0.010  5.017   0.545  0.193   0.183                       CH.sub.4+                                                                          93.5 0.900     0      93.5    0.900  0       0                           H.sub.2 S                                                                          1.3  0.258     0.078  0.0004  1.635  1.378   1.300                       TOTAL                                                                              100.0                                                                              1.511     0.088  98.517  3.080  1.571   1.483                   10                                                                                CO.sub.2                                                                           5.2  0.379     0.008  5.041   0.547  0.168   0.159                       CH.sub.4+                                                                          93.5 0.902     0      93.5    0.902  0       0                           H.sub.2 S                                                                          1.3  0.532     0.078  0.0004  1.909  1.378   1.300                       TOTAL                                                                              100.0                                                                              1.813     0.086  98.541  3.358  1.545   1.459                   11                                                                                CO.sub.2                                                                           5.2  0.406     0.007  5.065   0.548  0.142   0.135                       CH.sub.4+                                                                          93.5 0.905     0      93.5    0.905  0       0                           H.sub.2 S                                                                          1.3  0.916     0.078  0.0004  2.293  1.378   1.300                       TOTAL                                                                              100.0                                                                              2.227     0.085  98.565  3.746  1.520   1.435                   12                                                                                CO.sub.2                                                                           5.2  0.433     0.006  5.089   0.550  0.117   0.111                       CH.sub.4+                                                                          93.5 0.907     0      93.5    0.907  0       0                           H.sub.2 S                                                                          1.3  1.494     0.078  0.0004  2.871  1.378   1.300                       TOTAL                                                                              100.0                                                                              2.834     0.084  98.589  4.328  1.495   1.411                   13                                                                                CO.sub.2                                                                           5.2  0.460     0.005  5.113   0.551  0.092   0.087                       CH.sub.4+                                                                          93.5 0.910     0      93.5    0.910  0       0                           H.sub.2 S                                                                          1.3  2.459     0.078  0.0004  3.836  1.377   1.300                       TOTAL                                                                              100.0                                                                              3.829     0.083  98.613  5.297  1.469   1.387                   __________________________________________________________________________

                                      TABLE VI                                    __________________________________________________________________________    CONDITIONS                                                                        First Kettle                                                                        Second Kettle                                                                         Solvent:Acid Gas                                                                       Solvent Circulation                                                                      H.sub.2 S Product                                                                       CO.sub.2 Passed               Run #                                                                             (52) (°F.)                                                                   (54) (°F.)                                                                     (GAL/SCF)                                                                              (GAL/100 moles feed)                                                                     (mole %) (mole %)                       __________________________________________________________________________    14  235   245     1.3854   53,252     98.80     97.17                         15  240   245     1.3854   89,273     99.29     98.33                         16  244   245     1.3854   251,417    99.68     99.27                         17  235   245     1.3854   52,584     98.28     90.33                         18  240   245     1.3854   52,584     98.12     90.33                         19  244   245     1.3854   52,584     97.47     90.33                         __________________________________________________________________________

                                      TABLE VII                                   __________________________________________________________________________    MATERIAL BALANCES (moles)                                                              Stream No.                                                           Run      94   60        42     96      26     40      90                      No.      Feed Gas                                                                           First Stripper OHP                                                                      Lean Solvent                                                                         Absorber OHP                                                                          Rich Solvent                                                                         1st Stripper                                                                          2nd Stripper            __________________________________________________________________________                                                          OHP                     14                                                                                CO.sub.2                                                                           30   2.27      0.044  29.15   3.16   0.896   0.85                        H.sub.2 S                                                                          70   38.03     4.205  0.0001  112.24 74.205  70.0                        TOTAL                                                                              100  40.30     4.249  29.1501 115.40 75.101  70.85                   15                                                                                CO.sub.2                                                                           30   2.65      0.026  29.50   3.18   0.530   0.500                       H.sub.2 S                                                                          70   132.55    4.205  0.0001  206.76 74.206  70.0                        TOTAL                                                                              100  135.20    4.231  29.5001 209.94 74.736  70.50                   16                                                                                CO.sub.2                                                                           30   2.96      0.012  29.78   3.20   0.233   0.221                       H.sub.2 S                                                                          70   559.43    4.205  0.0001  633.64 74.205  70.0                        TOTAL                                                                              100  562.39    4.217  29.7801 636.84 74.438  70.221                  17                                                                                CO.sub.2                                                                           30   2.11      0.04   27.1    2.94   0.83    0.79                        H.sub.2 S                                                                          70   24.64     2.72   .0001   72.72  48.08   45.36                       TOTAL                                                                              100  26.75     2.76   27.1001 75.66  48.91   46.15                   18                                                                                CO.sub.2                                                                           30   2.44      0.02   27.10   2.92   0.49    .46                         H.sub.2 S                                                                          70   45.81     1.45   .0001   71.45  25.64   24.19                       TOTAL                                                                              100  48.25     1.47   27.1001 74.37  26.13   24.65                   19                                                                                CO.sub.2                                                                           30   2.70      0.01   27.10   2.91   0.21    .20                         H.sub.2 S                                                                          70   62.22     0.47   .0001   70.47  8.25    7.78                        TOTAL                                                                              100  64.92     0.48   27.1001 73.38  8.46    7.98                    __________________________________________________________________________

That which is claimed is:
 1. A process comprising:(a) contacting a firstgas stream containing CO₂, H₂ S and at least one hydrocarbon with asolution of at least one alkanolamine in a contacting zone; (b)withdrawing from the contacting zone a rich solution of at least onealkanolamine which is rich in H₂ S and CO₂ from the first gas stream;(c) introducing the rich solution into a separation zone; (d)selectively stripping the rich solution in the separation zone toproduce a second gas stream issuing from the separation zone whichcontains a higher CO₂ :H₂ S mole ratio than the first stream; and (e)conveying the second gas stream into an alkanolamine contacting zone. 2.A process as in claim 1 wherein the at least one hydrocarbon to betreated in the first gas stream contains from one to about 3 carbonatoms and wherein the alkanolamine contacting zone to which the secondgas stream is conveyed is the same zone as the contacting zone in whichthe first gas stream was contacted with the solution of at least onealkanolamine.
 3. A process as in claim 2 wherein the at least onealkanolamine is selected from the group consisting ofmethyldiethanolamine and n-propyldiethanolamine.
 4. A process as inclaim 3 wherein the first gas stream is contacted in the contacting zonewith between about 10 and 1000 moles of alkanolamine for each mole of H₂S which it contains.
 5. A process as in claim 4 wherein the alkanolaminesolution contains between about 5 and about 50 weight percent of thealkanolamine.
 6. A process as in claim 5 wherein conditions in thecontacting zone include a temperature within the range of 0°-100° C. anda pressure within the range of from about 0 to about 100 pounds persquare inch, gauge.
 7. A process as in claims 6 further comprisingwithdrawing a selectively stripped alkanolamine solution from theseparation zone which exhibits a higher H₂ S:CO₂ mole ratio than therich alkanolamine solution withdrawn from the contacting zone.
 8. Aprocess as in claim 7 wherein the alkanolamine comprisesmethyldiethanolamine.
 9. A process comprising:(a) contacting a first gasstream containing H₂ S, CO₂ and at least one hydrocarbon with a leanalkanolamine solution in a contacting zone; (b) withdrawing a richalkanolamine solution from the contacting zone which contains at least aportion of the H₂ S and CO₂ from the first gas stream; (c) introducingthe rich alkanolamine solution into a first stripping zone; (d)selectively stripping the rich alkanolamine solution in the firststripping zone to produce a second gas stream issuing from the strippingzone which contains a higher CO₂ :H₂ S mole ratio than the first gasstream; (e) withdrawing a selectively stripped alkanolamine solutionfrom the first stripping zone, said selectively stripped alkanolaminesolution containing a higher H₂ S:CO₂ mole ratio than the richalkanolamine solution from the contacting zone; (f) introducing theselectively stripped solution into a second stripping zone; and (g)stripping the selectively stripped solution to produce a third gasstream which is rich in H₂ S and lean in CO₂.
 10. A process as in claim9 further comprising withdrawing an alkanolamine solution from thesecond stripping zone which is lean in H₂ S and CO₂ and introducing thewithdrawn lean solution into the contacting zone for contacting thefirst gas stream.
 11. A process as in claim 10 further comprisingintroducing the second gas stream into the contacting zone for contactwith the lean alkanolamine solution.
 12. A process as in claim 11further comprising withdrawing a fourth gas stream from the contactingzone containing CO₂, at least one hydrocarbon, and a minor amount of H₂S, said fourth gas stream having a higher CO₂ :H₂ S mole ratio than thefirst gas stream.
 13. A process as in claim 12 wherein the alkanolamineis selected from the group consisting of methyldiethanolamine,n-propyldiethanolamine and mixtures thereof.
 14. A process as in claim13 wherein the at least one hydrocarbon in the first gas stream containsfrom one to about 3 carbon atoms.
 15. A process as in claim 14 whereinthe first gas stream further contains olefins and molecular hydrogen.16. A process as in claim 14 wherein the alkanolamine solution comprisesfrom about a 10 to about a 30 weight percent solution ofmethyldiethanolamine.